[R-sig-teaching] Shading the solution of quadratic inequality

[Randall Pruim]

The xlim=c(-6,-2) is extraneous in the code below.  It snuck in from  
something else I was doing.  It doesn't hurt any, but it doesn't do  
anything either since the plotting limits are inferred from the  
surrounding plot when add=TRUE is used.


On Feb 16, 2012, at 10:07 AM, Randall Pruim wrote:

> I'm not sure exactly what sort of plot was desired, but I'll offer  
> 1.5 possibilities.
>
> Currently you can do something like this:
>
> require(mosaic)
> plotFun( x^2 - 4 ~ x , xlim=c(-6,6), col='blue' )
> plotFun( (x^2 - 4)/as.numeric(x^2 -4 > 0) ~ x , xlim=c(-6,-2),  
> add=TRUE, col='blue', lwd=4 )
>
> It is a bit of kludge since I'm using division by 0 to hide part of  
> the function.  You can adjust colors, line thickness, and alpha to  
> your particular sensitivities.  And you can use type='h' if you want  
> a "filled in version".
>
> Soon, you should be able to do
>
> plofFun( x^2 - 4 ~ x, groups=(x^2-4>0) )
>
> If you find yourself wanting to plot "mathematical" functions like  
> this, I encourage you to give plotFun() a try and let us know how  
> you like it.
>
> ---rjp
>
>
> On Feb 16, 2012, at 9:42 AM, R. Michael Weylandt wrote:
>
>> You should probably say more about which graphics engine you are
>> using, but here's a start:
>>
>> curve(x^2-4, from = -3, to = 3)
>> x <- seq(-3, 3, length.out = 200)
>> polygon(c(x, rev(x)), c(x^2-4, rep(Inf, length(x))), col = 2)
>>
>> The red is a little "oppressive" so I'd try to add transparency if
>> your device supports it. Adding a shade above/below argument to curve
>> based on the same principles might be a fun exercise too...
>>
>> Michael
>>
>> On Thu, Feb 16, 2012 at 9:13 AM, AbouEl-Makarim Aboueissa
>> <aaboueissa at usm.maine.edu> wrote:
>>> Dear all R Users:
>>>
>>> How can I shade the solution (-Inf,-2) or (2,Inf) of the  
>>> inequality -x^2+4<0 within the curve of f(x)=-x^2+4.
>>>
>>> and
>>>
>>> the solution (-Inf,-2)or(2,Inf) of the inequality x^2-4>0 within  
>>> the curve of
>>> f(x)=x^2-4.
>>>
>>>
>>> with many thanks
>>>
>>> abou
>>>
>>>
>>> ==========================
>>> AbouEl-Makarim Aboueissa, Ph.D.
>>> Associate Professor of Statistics
>>> Graduate Program Coordinator
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>>> University of Southern Maine
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>>>
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